Method for treating phosphate rock



Feb. 10, 1942. J. HAGooD 2,272,799

A METHOD FOR TREATING PHOSPHATE ROCK v Filed 061'.. 25, 1959 Patented Feb. 10, 1942 ArEs PATENT OFFICE 2,272,799 METHOD Foa TREATING PHosPHA'rE ROCK Application October 25, 1939, Serial No. 301,307

(Cl. 'i1-46) 6 Claims.

This invention relates to heat conversion of phosphate rock to citrate-soluble or plant-available form.

Many proposals have been advanced in endeavors to provide a practicable method of converting raw phosphate rock `to plant-available forms by hea'. and reagents. Extensive experimentation over a period of years, during which the prior suggestions have been carefully and thoroughly tested, has proven that, while in some instances conversion of raw phosphate rock to plant-available form may be successfully accomplished on a laboratory scale, the suggested processes with which I am familiar cannot be successfully operated on a commercial scale. Actual tests of -production-scale operations have uniformly produced entirely uncontrollable and unpredictable results, thus, conversion during a commercial-scale run may be upon a satisfactory percentage at one time and within a half hour have fallen to an entirely unprotable percentage, with no apparent change in operating conditions. Similarly, the product at one time may be in a satisfactory physical condition, and at another time will be fused and entirely unsatisfactory,

even though temperature and reagent proportionsl where most carefully maintained constant.

As mentioned above, heat conversion of phosphate rock by use of alkaline reagents as heretofore proposed, may be readily accomplished on Y a laboratory scale. My experiments have led me l to the conclusion that it is the condition of the mass of material being treated that is responsible for the extremely variable results obtained when it Yis endeavored to carry out upon a commercial scale the methods that operate successfully in the laboratory.

In laboratory work, the mass of material treated is so small and may be so handled that uniformity of heating is accomplished, and satisfactory uniform conversion is obtained. Ap-

plication of identical conditions of heat, time and reagent proportions to large sized operations in rotary kilns have always produced the unsatisfactory results mentioned above. It is here to be noted that for reasons of economy of fuel and does not result in a thorough agitation and successive and uniform exposure of all particles at the surface', but tends to form a rotating mass in which there is little change of particles between the surface and the interior of the mass.

One object of this invention is to provide a novel method of heat treating a mixture of phosphate rock and reagent, whereby the entire mass of material is uniformly heated.

Another object is to uniformly heat a mixture of'phosphate rock and reagent in a continuous process. i

The essential feature of my invention is the discovery that if a mixture of phosphate rock and an alkaline reagent in a substantially planar,

relatively thin layer is subjected, during the heat-v ing thereof, to rabbling or like action such as will cause the particles of the mixture to move relative to one another, the material in the layer will be maintained ina loose, porous and gaspermeable condition and the material will be heated substantially uniformly throughout the layer and satisfactory conversion of the phosphate to a citrate soluble form will be obtained. The depth of the layer preferably is maintained uniform and the mixture of phosphate and alkaline reagent may be progressively moved through the heating zone while being brought to a temperature sufficiently high to effect the conversion in order to maintain the process continuous.

Advantageously, the method herein disclosed may be carried out in the apparatus disclosed in the accompanying drawing, which apparatus is at present regarded as preferable.

In the drawing:

Figure 1 is a vertical sectional View of an ap- I paratus for performing the process.

Figure 2 is a sectional view on line 2-21 of Figure 1.

Figure 3 is a detail vertical sectional view through one of the raking arms or rabbles.

Figure 4 is a detail vertical sectional view of one of the rakes.

The numeral 5 indicates a cylindrical, vertically disposed casing provided interiorly with ceramic insulation 6 of sufficient heat-resisting qualities to withstand the necessary high temperature. The furnace is provided with vertically spaced, horizontal, substantially planar hearths 1, advantageously three in number, and a horizontal, substantially planar bottom hearth 8. The hearths l are provided with openings 9, arranged in alternate hearths at their centers-and outer edges, for downward passage' of -the material undergoing treatment, and for upward passage of gases and products of' combustion. inlet III provides admission forthe mixture of phosfollowing mechanism, adapted to withstand heat of 24007 to 2500 F. vis employed. The bottom of the furnace and the lowest hearth 8 are provided with a central aperture I3 surrounded by a iiange I4 that depends from the bottom of the furnace. A vertical drive shaft I5, connected' with suitable power mechanism, extends toward the aperture I3 and carries a sand basin I8 into which the flange I4 depends to form a seal for the aperture. Upon the shaft l5, and rotating with it, is a tubular conduit I1 that extends vertically through the center of the furnace to a point above the top of the latter, the conduit being spaced from each of the hearths through which it passes.

A plurality of raking arms or rabbles I8 are supported upon and extendradially from the conduit II, such arms preferably being arranged in pairs that extend from opposite sides of the conduit and overlie the respective hearths. The arms I8 are hollow and their interiors communicate with the interior of the conduit I1. Each arm I8 is provided with a plurality of hollow raking teeth I9 that depend from the arms into close proximity to the surfaces of the hearths and have their interiors opening into theinteriors of the arms I8. The teeth are set atan angle with relation to their direction oftravel, and the teeth that operate over the alternate hearths are arranged at opposite angles, proper to urge the material over the hearths toward the openings that discharge to the succeeding hearth. Such arrangement is shown in Figure 2.`

The conduit Il, arms I81and teeth I9 are coated with a plastic insulating refractory 20 to protect them from the heat, and are water-cooled.

Water is introduced to the raking mechanism by means of a supply pipe 2I that leads in from above the furnace and is rotatably connected by a gland 22'with the upper end of the conduit Il, which surrounds it. The supply pipe 2l delivers cooling water to a tube 23 within and spaced from the conduit I1, which terminates adjacent the bottom of the furnace and below the surface of hearth 8 in a jet tube 24. Supply tubes 25, connected with the tube 23 extend into the respective rake arms I8, such tubes being spaced inwardly from the walls of said arms, being provided with nipples 26 that extend partially within and deliver jets into the interiors of the teeth I9. The tubes 25 are open-ended to deliver a stream of cold water into the spaces be-v tween their outer surfaces and the arms I8 additional to the water delivered into the teeth by the nipples 26.

It will be readily understood that when water is supplied by pipe 2|, it will be delivered by the tube 23 to the delivery tubes 25 and through the nipples 26 to the teeth 19, while by reason of the open ends of the tubes 25 and the jet tube 24,

. furnace, where, by means of exhaust pipes 21 it is delivered to altrough 28. A bell 29 carried by the conduit I1 depends into the trough 28 to seal the tcp of the furnace.A f

In order to provide heat, fuel burners are so arranged as to be capable of heating the lowermost hearth to a temperature sufllcient to eiect maximum conversion of the phosphatic material.

additional water is supplied to the interiors of the rake arms I8 andthe conduit I'I. The water is returned by conduit Il to a point above the It is considered preferable to use oil or other pressure burners 30 arranged to deliver flames tangentially of the lower hearth. Thenumber of burners may bevaried in accordance with the temperature required, and additional burners may be placed for operation upon hearths other than the lower one. i

Operation of the apparatus vwill be readily understood. `The burners 30 being red, the products of combustion after sweeping vover the hearth 8 flow upward, moving across alternate hearths in opposite-radial directions. A mixture of phosphate rock and reagentintroduced at I0 descends to the uppermost hearth where it is raked into a layer, and moved by the rabbles in a manner such that it is maintained in a loose, porous and gas-permeable' condition so that uniform heating of the material will bek obtained. Due to the arrangement of the teeth, the material is graduallyv swept toward the center of the hearth and descends to the next hearth where it is again spread in a layer and raked to move` and agitate it; the direction of motion upon the secondhearth being radially outward. As the material advances, it is swept by the oppositely travelling combustion products and progressively heated to the maximum. temperature upon the lower hearths. After the maximum heating, during which conversion will have occurred, the material is swept from the outlets II and discharged from the furnace.

The method and apparatus herein disclosed may be utilized in phosphate conversion according to different details of practice. advantageous to utilize a mixture of 6 percent sodium carbonate with phosphate rock and a temperature maximum between 2400" and 2500 F. It is generally understood that reagent proportion and temperature required are related in inverse proportion. The method and apparatus is capable of use with other desirable proportions of reagents and temperature ranges.

From the foregoing it is thought that the con struction, operation and many advantages of the method and apparatus of the herein disclosed invention will be readily apparent to those skilled in the art. It willbe understood that changes in size, shape, proportion and minor details of the apparatus, and alterations in the details of the method may be resorted to without departing from the spirit of the invention as set forth in the accompanying claims. It will be further apparent that the method herein described is capable of accomplishment by apparatus other than that herein described.

What I claim is:

1. The method of converting phosphate rock to a citrate soluble form which comprises subjecting a mixture of phosphate rock and an alkaline laali-metal compound to a temperature ciently high to effect such conversion while maintaining the mixture in a substantially horizontal, at layer of substantially -uniform thickness and simultaneously with said heating'subjecting the particles of the mixture to movement relative to one another such as to maintain the material inthe layer in a loose, porous and gas- I consider it l permeable condition, whereby the heating of the material is substantially uniform throughout the layer.

2. The method of converting phosphate rock to a citrate soluble form which comprises subjecting a mixture of phosphate rock and an alkaline reagent to a temperature of the order of 2400 to 2500 F. to effect such conversion While maintaining the mixture of phosphate rock and alkaline reagent in a substantially horizontal,

at layer of substantially uniform thickness, and` simultaneously with said heating subjecting the particles of the mixture to movement relative to sufficiently high to eiect conversion of the phos-A phate to a citrate soluble form, and subjecting the particles of the mixture in said layer, during the heating thereof, to movement relative to one another such as to maintain-the mass of material in the respective layers in a loose, porous and gas-permeable condition, whereby the heating of the material is substantially uniform throughout the respective layers.

4. The method of converting phosphate rock to a citrate soluble form which comprises-progressively conveying a mixture of phosphate rock and an alkaline alkali-metal compound over a series of substantially horizontal, fiat hearths, forming the mixture, as it passes over each hearth into a layer of substantially uniform thickness, heating the mixture as it progressively passes over said hearths to a temperature suciently high to effect conversion o f the phosphate to 'a citrate soluble form, and subjecting the material of the layers, during the heating thereof, to rabbling to maintain the mass of material in the respective layers in a loose, porous and gas-permeable condition, whereby the heating of the material is substantially uniform throughout the respective layers.,

5. The method of converting phosphate rock to a citrate soluble form which comprises progressively conveying a mixture of phosphate rock and an alkaline reagent over a series of substantially horizontal flat hearths, forming the mixture, as it passes over each hearth into a layer of substantially uniform thickness, heating the mixture as it progressively passes over said hearths to a temperature of the order of 2400 to 2500 F. to eiect conversion of the phosphate to a citrate soluble form, and subjecting the particles of the mixture in said layers, during the heating thereof, to movement( relative to one another such as to maintain the mass of material in the respective layers in a loose, porous and gas-permeable condition, whereby the heating of the material is substantially uniform throughout the respective layers.

6. The method of converting phosphate rock to a citrate soluble form which comprises progressively conveying a mixture of phosphate rock and an alkaline reagent over a series of substantially horizontal flat hearths, forming the mixture, as it passes over each hearth into`a layer of substantially uniform thickness, heating the mix- 

